Generally, in telecommunication networks, data concerning the subscribers using the services are permanently stored in a home location register HLR of a respective user.
Note that throughout the following specification, following the definition as given in GSM 03.08, Version 4.8.0, page 9, the term user data will be used to designate all information associated with a subscription which is required for service provisions, identification, authentication, routing, call handling, charging, subscriber tracing, operation and maintenance purposes. Some subscriber data are referred to as permanent subscriber data, i.e. they can only be changed by administration means. Other subscriber data are referred to as temporary subscriber data which may change as a result of normal operation of the system.
Each subscriber is assigned to a specific HLR of the network he has subscribed to, i.e. the network (PLMN) operated by his network operator with whom he has a service contract. Note that each PLMN network has at least one HLR, depending on the number of actual subscribers to the network.
However, the HLR as a database represents too slow a storage means in terms of access times for the management of the subscriber data upon, e.g. a call connection request.
Therefore, visitor location registers VLR for a dynamic subscriber data management were introduced. In VLR's, a copy of at least part of the subscriber data for a respective subscriber is included. Moreover, a respective VLR is associated with a corresponding geographical area of the telecommunication network PLMN it belongs to. Hence, only those subscriber data are present in the VLR which correspond to the subscribers presently present in the geographical area of the VLR.
Among the subscriber data which could be considered most important, the following are for example contained in both, the HLR as well as the VLR:
1) Subscriber specific data:                IMSI (International Mobile Subscriber Identity), TMSI (Temporary Mobile Subscriber Identity), Supplementary Services indication parameters available for the subscriber, and a basic MSISDN (Mobile Station ISDN number, i.e. the basic telephone number of the subscriber)        
2) Authentication and Ciphering data:                RAND/SRES/Kc parameters (up to five triplets of the parameters)        
3) Subscriber location/Call forwarding parameters:                MSC number (Mobile Services Switching Center), and LMSI (Local Mobile Station Identity).        
For a more detailed but still general introduction to the HLR/VLR interdependency it is referred to Gunnar Heine: “GSM Networks: Protocols, Terminology, and Implementation”; Chapter 4: “The Network Switching Subsystem”; pp. 31 to 35; Artech House Mobile Communications Library; Artech House Publishers, Boston, London; 1999.
Hitherto, in connection with subscriber data management at the HLR/VLR, every time a subscriber enters to a new geographical area associated to a different (i.e. “new”) VLR and served by the new VLR and the MSC's associated thereto, the subscriber data were downloaded and/or transferred from the “old” VLR the geographical area of which has been left to the new VLR the geographical area of which has been entered. Also, there may arise situations, in which the subscriber data of the roaming/moving subscriber is not transferred from the old VLR, but has to be downloaded from the subscriber's home HLR (i.e. the HLR of the PLMN he has subscribed to). In the above cases, the subscriber data were deleted from the old VLR upon the subscriber having left the geographical area corresponding to the VLR.
Apparently, if the geographical areas associated with the VLR's are quite small, or the subscriber frequently moves “between different VLR's”, the data transfer between respective VLR's and/or between the subscriber's HLR and the VLR's will represent a large signaling load. This holds for subscribers moving within their home network as well as for roaming subscribers (moving between different networks, particularly, between different international networks established in different countries), so that due to the large amount of necessary signaling, correspondingly high signaling costs will accrue.
Additionally, with a continuous growth of international traveling for business purposes and/or holidays, the number of roaming subscribers can be expected to increase significantly in the future, so that the above problem will become even more severe.
In consequence, an attempt referred to as Super Charger has been made to reduce the signaling load and the signaling costs inherent thereto. For the purposes of the present invention, the Super Charger feature is not set out in detail herein, but the interested reader is expected to be familiar with the Super charger feature.
That is, in this attempt it has been proposed to equip a network with the Super Charger feature (so-called Super-Charged Network) so that in such a Super-Charged network subscriber information is no longer deleted from the VLR databases when a mobile station leaves the geographical area associated with the respective VLR/MSC's it has registered to.
However, this will lead to a continuous growth of the size of the VLR database. In consequence, a VLR database, in order to handle and/or keep the large amount of subscriber data which are no longer deleted, could become as large as a HLR database. This, however, could lead to a drawback such that the access speed of the VLR database is no longer superior to the access speed of a HLR, so that the VLR could no longer fulfill its task of a quick dynamic subscriber data management for call control and/or mobility management purposes.
Therefore, some VLR database management functionality has to be provided for in order to prevent the necessity for provisioning a VLR database of excessive size.
In a most recent proposal made by NORTEL NETWORKS in the 3GPP TSG-CN Workgroup 2 meeting in Edingurgh, U.K., May 17–21, 1999, a basic database management method is proposed. Apart from the utilization of larger databases, a deletion of subscriber data, either in a periodic audit or in the course of a dynamic subscriber data deletion, is proposed. Such a deletion of subscriber data as proposed by NORTEL is, however, solely based on the age of the subscriber data, such that in either case the oldest data are removed first from the VLR database.
Such a VLR database management procedure, however, is not an optimum one.